This invention relates to a dynamoelectric machine and more particularly to an air gap baffle assembly for a turbine generator.
As is well known, large dynamoelectric machines such as turbine generators, produce heat when they are in operation due to the internal losses of the machine. To keep the machine operating within desirable temperature limits, a cooling gas such as hydrogen is forced through the machine to carry away the heat. Most large dynamoelectric machines have provisions for the necessary blower assemblies, heat exchangers, and coolant passageways to ensure adequate circulation of the coolant gas which maintains the temperature of the machine within acceptable operating limits. In order to keep the stator bore and the outer region of the rotor body (the area being commonly referred to as the air gap, whether or not air is the cooling gas) within these temperature limits, a fixed amount of cooling gas such as hydrogen is required to flow axially through the air gap. Since the blower on the dynamoelectric machine operates at the required pressure and associated volumetric flow rate, to ensure adequate cooling of the entire machine, the cooling gas flowing through the air gap must be regulated to a predetermined flow rate. The standard means of regulation is a restrictive device or baffle inserted at the entrance of the air gap area. This device must provide a preset controllable entrance area to the air gap with a minimum amount of leakage through secondary passages.
FIGS. 1 and 2 are schematic diagrams of one such prior art baffle design. FIG. 1 is a partial section view of a stator assembly, and a baffle ring. FIG. 2 is an end view of the baffle ring and a rotor, wherein the stator is removed.
In FIG. 1 of the prior art the portions of the stator assembly 100 that are shown include an end pack 105, a finger plate 102 and a stator winding 103. A prior art baffle ring 104 is seated approximately one inch into the bore of the machine where a seal is made between the ring 104 and the end pack 105; said seal being, for example, an impregnated dacron pad 112. The baffle ring is held in place by inserting under every other coil of the stator winding 103, another resin impregnated dacron pad 113; and then tying the baffle ring 104 in place with rope ties (not shown) which are secured to the stator end turns through holes 110. The regulation of gas flowing through the air gap is controlled through the use of a neoprene rubber insert seal 108. Because the installation and removal of the rotor assembly necessitates the insertion of tools beneath the rotor, there is a keystone area 107 cut out of the seal 108.
On the previous design as shown in FIGS. 1 and 2, a seal is made between the ring 104 and the stator bore at the point where the baffle ring 104 is seated. The seal was made by an impregnated dacron felt pad 112 as was discussed above. Since the quality of the seal depended upon the skill of the workmen, the secondary leakage area was somewhat undeterminable, and variable from machine to machine. It was difficult to apply the dacron felt pad 112 and, at the same time, hold the baffle ring 104 in a desired axial and radial location.
Another drawback with the prior design is that the baffle ring covered some of the stator iron, iron that is relatively easily damaged since it is at the end of the stator bore. There are other problems encountered by covering the end pack of the stator assembly. For example, inspection by the use of thermovision is very difficult. Also, as dynamoelectric machines have increased in size, it has become necessary to provide radial vents in the first end pack of the stator core for additional cooling. Of course this is made more difficult with the prior art baffle ring located radially inward of the end pack.
Furthermore, an important design criterion is that the rotor be accessible to permit use of assembly and disassembly tooling. In order to do this, a keystone notch 107 at the base of the baffle ring 104 was provided. In a machine with a large air gap, the entrance area in the region of keystone opening 107 may become so large as to impede the regulation of cooling gas flow.
Still another problem is the manufacturing difficulties associated with the installation of the rubber sealant, due to the resin filling and heating cycle.
Desirable therefore is a new design for the air gap baffle assembly; one that permits access to the rotor for assembly tooling, while at the same time permits simpler manufacturing, assembly and servicing techniques.